disable mlx5 driver in skiroot_defconfig

Quite simply, the driver doesn't work properly. It's a kexec disaster
and without (yet another) patch we have to carry locally, it's not
going to work for the imminent op-build v1.10.

We'll think about re-enabling this once the appropriate patches make
it to the Linux stable tree.

Fixes: https://github.com/open-power/op-build/issues/538
Reverts: https://github.com/open-power/op-build/pull/479
Reverts: 17b4c3c6e6389c8d5d354ef778ce1f39067f8a34
Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>
diff --git a/openpower/configs/linux/skiroot_defconfig b/openpower/configs/linux/skiroot_defconfig
index bb1e33f..688524d 100644
--- a/openpower/configs/linux/skiroot_defconfig
+++ b/openpower/configs/linux/skiroot_defconfig
@@ -139,8 +139,6 @@
 CONFIG_IXGBE=m
 CONFIG_NET_VENDOR_MELLANOX=y
 CONFIG_MLX4_EN=m
-CONFIG_MLX5_CORE=m
-CONFIG_MLX5_CORE_EN=y
 CONFIG_MYRI10GE=m
 CONFIG_QLGE=m
 CONFIG_NETXEN_NIC=m